Information storage apparatus storing and reading information by irradiating a storage medium with electron beam

ABSTRACT

To greatly increase the storage density of a storage apparatus, an electron beam E emitted from a cold cathode  101  is accelerated by an accelerating electrode  102 , caused to converge by a convergence electrode  103 , deflected by a deflection electrode  104  and applied to a minute region of a storage film  105 . The storage film  105  includes, for example, a phase change film  105   a . The film is rapidly heated and cooled to change into an amorphous state upon irradiation with an electron beam E with high energy, while being gradually cooled to change into a crystallized state upon irradiation with an electron beam E with approximately intermediate energy, thereby storing data. Upon irradiation with an electron beam E with low energy, the potential difference between a detection electrode  105   b  and an anode  105   c  is detected depending on the state, i.e., the amorphous or crystallized state, thereby reading stored data.

TECHNICAL FIELD

The present invention relates to a technique for an information storageapparatus that stores and reads information by irradiating a storagemedium with an electron beam.

BACKGROUND ART

As an information storage apparatus that stores and reads information byirradiating a dielectric with an electron beam, an apparatus using acathode ray tube (CRT) similar to that for display had been studied muchbefore core memories and semiconductor memories were put into practicaluse (for example, U.S. Pat. No. 2,755,994, column 2, lines 19 to 56.) Inthis patent, as in the case of displaying an image, a voltage ofnegative several thousand volts is applied to a red hot filament so asto emit thermoelectrons, and a dielectric (phosphor) is irradiated withan electron beam of the thermoelectrons, thereby storing and readinginformation.

More specifically, when a region of a dielectric associated with astorage bit is irradiated with a deflected electron beam, electronavalanche occurs in the irradiated region and electrons in thedielectric are emitted. In this state, the irradiated region becomesdeficient in electrons. If the irradiation with the electron beam isstopped at this time, this electron deficiency state is maintained. Onthe other hand, if similar irradiation with an electron beam isperformed from the region associated with the storage bit to itsneighboring region according to scanning with the electron beam,electron avalanche also occurs in the neighboring region so that emittedelectrons move to the region associated with the storage bit. At thistime, the electron deficiency in the region associated with the storagebit is eliminated and the region changes into an indeficiency state.Then, this indeficiency state is maintained. That is, data “0” or “1” isstored by maintaining the electron deficiency or indeficiency state asdescribed above.

As described above, when the region in the electron indeficiency stateis irradiated with an electron beam and thereby changes into adeficiency state, the potential at a pickup plate provided on a tubeface of a CRT varies depending on the change of the state. On the otherhand, even when the region already in the deficiency state is irradiatedwith an electron beam, such a potential variation does not occur.Accordingly, stored data is read out by detecting a potential change (orcurrent flowing due to the change) at the pickup plate.

—Problems to be Solved—

However, conventional information storage apparatuses as described aboveutilizing irradiation with electron beams have been replaced with corememories and then semiconductor memories, and are now not used at allbecause of the following reasons:

(1) The sizes of apparatuses themselves are large;

(2) Heaters and power supplies for the heaters are needed to emitthermoelectrons; and

(3) High voltages of about several thousand volts are required to emitelectron beams.

On the other hand, the semiconductor memories currently used in generalhave their sizes greatly reduced and storage densities greatlyincreased, as compared to the information storage apparatuses utilizingirradiation with electron beams. However, semiconductor processes haveconstraints in fabrication, and therefore there arises the problem ofdifficulty in achieving a much higher density.

In view of this, it is therefore an object of the present invention togreatly increase the storage density so as to store a large amount ofinformation.

DISCLOSURE OF INVENTION

To solve the foregoing problems, according to the present invention, aninformation storage apparatus including:

-   -   a cold cathode electron beam emitting part;    -   a flat anode opposed to the cold cathode electron beam emitting        part; and    -   a storage medium formed on the front or back of the anode and        used for storing and reading information in accordance with        irradiation with an electron beam emitted from the cold cathode        electron beam emitting part has the following features.

The cold cathode electron beam emitting part may include a cold cathodeplaced in a chamber surrounded by a partition and a film capable oftransmitting an electron beam such that the inside of the chamber has ahigher degree of vacuum than the outside thereof. In such a case, thedegree of vacuum around a spindt-type cold cathode or carbon nanotubes,for example, is maintained and attachment of foreign matters and othersare prevented with ease. Accordingly, even in the cases of a spindt-typecold cathode and a small number of carbon nanotubes, the beam spot sizeis more easily reduced so that the storage density is increased withoutdecrease in stability of electron emission.

Furthermore, in a case where an accelerating part for accelerating anelectron beam emitted from the cold cathode electron beam emitting part,a deflection part for deflecting the electron beam in one- ortwo-dimensional directions, and a convergence part for causing theelectron beam to converge are provided with a given electric field ormagnetic field generated, an electron beam may be accelerated in such amanner that a plurality of electrodes to which voltages with differentphases are applied are provided and thereby a moving electric field isgenerated. The cold cathode electron beam emitting part may beconfigured in such a manner that a plurality of electron emitting partsare provided to emit electron beams at different timings according tothe distance from a given center so that the emitted electron beamsconverge. With these configurations, the presence and absence ofemission of an electron beam, the energy thereof and an irradiatedposition and an irradiated area on the storage medium, for example, areeasily controlled.

To irradiate only a given region of the storage medium with an electronbeam, an electron beam passing through a minute hole formed in ashielding part such as a plate member may be adjusted to reach thestorage medium. If at least one of such a plate member and the storagemedium is moved by an actuator using a so-called micromachinetechnology, reduction of an area of the storage medium irradiated withan electron beam and control of the irradiated position are also easilyachieved. An electrode may be provided around the minute hole to form anelectrolytic lens. Then, the efficiency in using an electron beam isenhanced and, in addition, a region irradiated with an electron beam issmaller than the diameter of the minute hole, thus further increasingthe storage density.

A plurality of electron beams may be emitted to fall on a plurality ofregions of the storage medium so that a plurality of bits of informationis stored or read out at the same time. Accordingly, storage and readingare performed at higher speed.

An irradiated-position-shift detecting part for detecting a shiftbetween a given reference position and a position in the storage mediumirradiated with an electron beam may be provided so that the irradiatedposition is controlled by calibration or feedback control. Then, theaccuracy in locating the irradiated position is enhanced, and thestorage density is more easily increased.

Part of information stored and read out at the same time may be used forerror detection or error correction.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram illustrating a configuration of an informationstorage apparatus including one information storage cell.

FIG. 2 is a perspective view illustrating an example of an acceleratingelectrode 102.

FIG. 3 is a side view illustrating an example of a cold cathode 101.

FIG. 4 is a side view illustrating another example of the cold cathode101.

FIG. 5 is a side view illustrating yet another example of the coldcathode 101.

FIG. 6 is a side view illustrating still another example of the coldcathode 101.

FIG. 7 is a side view illustrating still another example of the coldcathode 101.

FIG. 8 is a cross-sectional view illustrating still another example ofthe cold cathode 101.

FIG. 9 is a cross-sectional view illustrating an example of a ballisticelectron emitting element.

FIG. 10 is an illustration showing an example in which a componentserving as both the accelerating electrode 102 and a convergenceelectrode 103 is used.

FIG. 11 is an illustration showing an example in which a componentserving as both the accelerating electrode 102 and a deflectionelectrode 104 is used.

FIG. 12 is a front view illustrating an example of an electrode servingas both of the accelerating electrode 102 and the deflection electrode104.

FIG. 13 is an illustration showing an example of annular electrodes 302for generating a moving electric field.

FIG. 14 is a side view illustrating an example of the cold cathode 101for emitting an electron beam which will converge.

FIG. 15 is an illustration showing another configuration for controllinga region irradiated with an electron beam.

FIG. 16 is an illustration showing yet another configuration forcontrolling a region irradiated with an electron beam.

FIG. 17 is a perspective view showing a configuration of an informationstorage apparatus including a plurality of information storage cells.

FIG. 18 is a block diagram showing a connection relationship amongcathode ray drivers and other elements in the information storageapparatus including the plurality of information storage cells.

FIG. 19 is an illustration showing a configuration of a servo cell forcontrolling a position irradiated with an electron beam.

FIG. 20 is an illustration showing an example in which some of theinformation storage cells are used for error correction.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present invention will be described withreference to the drawings.

(Information Storage Apparatus Including One Information Storage Cell)

FIG. 1 is a view schematically showing a configuration of an informationstorage apparatus including one information storage cell 100.

A cold cathode 101 emits an electron beam E upon application of anegative voltage from a cathode ray driver 111. The configuration ofthis cold cathode 101 will be specifically described later. The voltageapplied to the cold cathode 101 may be a DC voltage or a pulse drivingvoltage such as surge pulses.

An accelerating electrode 102 is made of an annular electrode as shownin FIG. 2, for example, and receives, from an acceleration controllingcircuit 112, a voltage higher than that applied to the cold cathode 101.The accelerating electrode 102 extracts electrons from the cold cathode101 by utilizing an electric field generated between the acceleratingelectrode 102 and the cold cathode 101 and accelerates the electrons.

As the accelerating electrode 102, a convergence electrode 103 is madeof an annular electrode. Upon application of a given voltage from aconvergence controlling circuit 113, the convergence electrode 103generates an electric field serving as a lens with respect to theelectron beam E, and causes the electron beam E emitted and divergingfrom the cold cathode 101 to converge.

The deflection electrode 104 includes a pair of opposed electrode plates104 a and 104 b and deflects the electron beam E for scanning uponapplication of different voltages to the respective electrode plates 104a and 104 b from a deflection controlling circuit 114. In this case, apotential difference generator 114 a shown in FIG. 1 controls thepotential difference between the electrode plates 104 a and 104 b. Inthe case of deflecting the electron beam E in two-dimensionaldirections, two pairs of deflection electrodes 104 may be provided.

A storage film 105 includes: a phase change film 105 a changing into anamorphous state or a crystallized state according to the degree ofheating and cooling; a detection electrode 105 b provided on the side ofthe phase change film 105 a toward the cold cathode 101; and an anode105 c provided on the opposite side of the phase change film 105 a. Theanode 105 c is grounded and the detection electrode 105 b is connectedto a signal regenerator 115 to detect the potential difference betweenthe detection electrode 105 b and the anode 105 c. The size and pitch ofa storage region for one bit in the storage film 105 is determined inaccordance with permissible accuracies (variations) in the amount ofdeflection and the degree of convergence of an electron beam.

The cathode ray driver 111, the acceleration controlling circuit 112,the convergence controlling circuit 113 and the deflection controllingcircuit 114 are configured by using D/A converters, for example. On theother hand, the signal regenerator 115 is configured by using an A/Dconverter.

In the information storage apparatus thus configured, information isstored and read out in the following manner.

When a potential difference at a given level or higher is applied acrossthe cold cathode 101, and the accelerating electrode 102, electrons areemitted from the cold cathode 101, accelerated by the acceleratingelectrode 102, caused to converge by the convergence electrode 103, andthen deflected by the deflection electrode 104, thereby irradiating aminute region of the storage film 105 with an electron beam E. At thistime, if the detection electrode 105 b has a resistance higher than thatof the phase change film 105 a, current flows into the anode 105 c andhardly diffuses through the detection electrode 105 b and the phasechange film 105 a.

In this case, when a voltage applied to the cold cathode 101 or theaccelerating electrode 102 is controlled such that the potentialdifference therebetween is higher than or equal to a given level tosupply high energy to the electron beam E, the phase change film 105 ais rapidly heated. Then, when the electron beam E is shut off by settingthe potential difference between the cold cathode 101 and theaccelerating electrode 102 at zero, for example, after a lapse of timeenough to heat the phase change film 105 a to a given temperature, theelectron-beam irradiated region of the storage film 105 is rapidlycooled, so that the phase change film 105 a changes into an amorphousstate. On the other hand, when the potential difference between the coldcathode 101 and the accelerating electrode 102 is set at a level lowerthan the above level to reduce the energy of the electron beam E, thephase change film 105 a is heated to a temperature lower than that inthe case of high energy. When the electron beam E is shut off, thisheated phase change film 105 a is gradually cooled to be crystallized.By changing the phase change film 105 a into the amorphous state and thecrystallized state with different energies of the electron beam E asabove mentioned, data “0” or data “1” is stored. In the case ofcrystallization, the energy of the electron beam E may be graduallylowered, for example.

The phase change film 105 a has different resistance values between theamorphous state and the crystallized state. Accordingly, the potentialdifference between the detection electrode 105 b and the anode 105 cupon irradiation with an electron beam E at a low energy level at whichthe state of the phase change film 105 a does not change is larger inthe case of the amorphous state than in the case of the crystallizedstate. In view of this, the potential difference is detected by thesignal regenerator 115, thereby reading stored information.

The position in the phase change film 105 a irradiated with the electronbeam E is controlled at high speed by a voltage applied to thedeflection electrode 104. That is, no mechanical elements such as a harddisk and an optical disk are not included, so that it is possible tostore and read information at an extremely high speed. A sawtooth wavemay be applied to the deflection electrode 104 so as to scan the storagefilm 105 with an electron beam E. If a voltage which changes stepwise isapplied, random access is obtained, so that access is performed at ahigher speed.

(Specific Configuration of Cold Cathode 101)

Examples of the cold cathode 101 include: a spindt-type cathode having asharp point and made of, for example, tungsten, silicon or diamond; acathode using a carbon nanotube; and a cathode using a ballisticelectron emitting element. In particular, in the cases of using thecathode using a carbon nanotube and the cathode using a ballisticelectron emission element, an electron beam E is easily generated evenwith a potential difference between the cold cathode 101 and theaccelerating electrode 102 of 10V or less. Accordingly, powerconsumption is greatly reduced and, in addition, a large amount ofminiaturization of the entire structure is more easily achieved.

More specifically, as shown in FIG. 3, the cold cathode 101 using acarbon nanotube is configured in such a manner that one carbon nanotube101 b is provided to stand on a base 101 a made of, for example,conductive silicon. If the carbon nanotube 101 b is provided in thisway, the electron emission source is a point electron source, so thatthe spot size in a region of the storage film 105 irradiated with anelectron beam is reduced to a diameter of about several nanometers.Accordingly, suppose a recording point associated with one bit has adiameter of about 8 nm, if 128×128 recording points are arranged on a 1μm-square recording face, 16 Kbits of information is stored.

Alternatively, the cold cathode 101 may include a plurality of carbonnanotubes. For example, as shown in FIG. 4, carbon nanotubes 101 bextending in random directions may be provided on the base 101 a. Thecold cathode 101 having such a configuration is easily formed at a lowcost by, for example, applying a solution in which carbon nanotubes aredispersed. In addition, such a cathode includes a large number ofelectron emitting edges, so that electrons are easily emitted withstability even at a relatively low degree of vacuum. In order to reducethe beam spot size in the presence of the carbon nanotubes 101 b on arelatively large area of the base 101 a, the convergence electrode 103and other components only need to be set at high accuracy as in aconverging optical system or the like. Alternatively, as shown in FIGS.5 and 6, several carbon nanotubes 101 b may be provided by vapordeposition or other processes to locally stand on a region with adiameter of 100 nm or less. In these cases, electron emission morestable than in the case of providing one carbon nanotube 101 b is easilyperformed. In addition, the beam spot size is relatively easily reducedby making an electron emission source closer to a point electron source.Furthermore, as shown in FIG. 7, a large number of carbon nanotubes 101b having substantially the same length may be densely arranged insubstantially the same direction. In this case, more stable emission ofelectrons is easily performed and fabrication is relatively easilyperformed.

Moreover, as shown in FIG. 8, for example, the cold cathode 101 may beplaced in a chamber surrounded by a partition 201 and a film 202 of athin film made of, for example, gold with a high ductility and capableof transmitting an electron beam such that the inside of the chamber hasa higher degree of vacuum than the outside thereof. Specifically, it isnot always easy to maintain a high degree of vacuum between the coldcathode 101 and the storage film 105 because molecules are readilyscattered during collision of electrons with the storage film 105.However, if the cold cathode 101 is placed in the small chamber asdescribed above, the space surrounding the cold cathode 101 is kept at ahigh degree of vacuum and adhesion of foreign matters to the coldcathode 101 is prevented, so that stable emission of electrons isperformed even in the case of providing a small number of carbonnanotubes. Accordingly, the beam spot size is more easily reducedwithout decrease in stability of electron emission. In the foregoingconfiguration, a conductive film may be used as the film 202 to alsoserve as the accelerating electrode 102.

In addition, a ballistic electron emitting element that may replace thecold cathode 101 as described above is obtained by, for example, formingsilicon impalpable particles 204 in a minute cavity 203 with a diameterof about 100 nm or less as shown in FIG. 9. In the case of using such aballistic electron emitting element, stable emission of a high-energyelectron beam is easily achieved.

(Configuration of Accelerating Electrode 102 and Other Components)

The accelerating electrode 102, the convergence electrode 103 and thedeflection electrode 104 are not limited to the above-describedelectrodes including the annular electrodes and opposed electrodes andmay be cylindrical electrodes, coils for generating magnetic fluxes, orany combination of such electrodes and coils. In addition, a pluralityof convergence electrodes 103 may be provided to generate a desiredelectric field with higher accuracy.

In addition, as shown in FIG. 10, for example, only one of theaccelerating electrode 102 and the convergence electrode 103 may beprovided and have functions of accelerating the electron beam E andcausing the electron beam E to converge upon application of a positivevoltage to the cold cathode 101.

Furthermore, as shown in FIGS. 11 and 12, an annular electrode 301 maybe divided into four so as to replace both of the accelerating electrode102 and the deflection electrode 104. In addition, if the averagepotential of the divided electrodes 301 a through 301 d is higher thanthat of the cold cathode 101 and the divided electrodes 301 a and 301 band/or the divided electrodes 301 c and 301 d have a potentialdifference/potential differences, i.e., if the relative potentials ofthe respective divided electrodes 301 a through 301 d are controlled,the electron beam E is accelerated and deflected. (In the case ofdeflecting the electron beam E only in one-dimensional directions, forexample, the annular electrode 301 only needs to be divided into two.)

Alternatively, a component serving as both the convergence electrode 103and the deflection electrode 104 may be used. (In this case, it can beconsidered that adjustment of relative potentials moves the center of anequivalent electron lens so that the focal point of an electron beamshifts in the X-Y direction.) Furthermore, a component serving as theaccelerating electrode 102, the convergence electrode 103 and thedeflection electrode 104 may be used with a positive voltage applied tothe divided electrodes 301 a through 301 d as described above. That is,the components such as the accelerating electrode 102 do not necessarilyneed to be physically separated and it is sufficient for thesecomponents to have the above functions as a whole.

If an electron beam E with sufficient energy is obtained by using thepotential difference between the cold cathode 101 and the storage film105, it is unnecessary to provide the accelerating electrode 102.

As shown in FIG. 13, for example, a plurality of annular electrodes 302may be provided such that pulse voltages with different phases aresequentially applied to generate a moving electric field and therebyaccelerate the electron beam E. In this case, the generated electrodebeam E has high coherence with, i.e., the same speed and same phase as,the moving electric field. Accordingly, the beam spot size is moreeasily reduced.

Furthermore, as shown in FIG. 14, for example, carbon nanotubes 101 bdensely arranged to form a plane may be divided into a plurality ofregions, e.g., concentric regions, and electron-beam generating pulsevoltages with different delay times may be applied to the respectiveregions of the carbon nanotubes 101 b. Then, the electron beam Econverges according to a principle similar to that in a phased arrayradar.

(Other Configurations for Controlling Region Irradiated with ElectronBeam E)

Instead of convergence and deflection of an electron beam E as describedabove, at least one of a shielding plate 401 in the shape of a platehaving a minute hole 401 a (pin hole) and the storage film 105 may bemoved by an actuator 402, as shown in FIG. 15, for example. The actuator402 may be constructed by an electrostatic actuator unit and an elasticmember, for example. If two pairs of electrostatic actuator units andothers are used, a two-dimensional drive is easily performed.

By shielding an electron beam E by using the shielding plate 401 asdescribed above, control of a region irradiated with the electron beam Eis ensured and the storage density is easily increased. In addition, anelectron emitting part of the cold cathode 101 does not need to be verysmall, so that stable emission of electrons is easily achieved. Inaddition, the configuration is simplified because the convergenceelectrode 103 and other components are not needed. However, theconvergence electrode 103 and other components may be provided toenhance the energy of the electron beam and to perform convergence anddeflection of the electron beam so that the efficiency in utilizing theelectron beam is increased. Even in such a case, the region irradiatedwith the electron beam is accurately controlled by the shielding plate401, so that the accuracy in controlling convergence and deflection doesnot need to be maintained at such a high level.

In a case where the shielding plate 401 is placed at a fixed positionwith respect to the cold cathode 101 and the storage film 105 is moved,the configuration of the movable part is easily simplified because thestorage film 105 is located at the outside of the shielding plate 401.Alternatively, since the relative positions of the cold cathode 101 andthe shielding plate 401 do not change, the cold cathode 101 and theshielding plate 401 may be united so as to simplify the configurationand fabricate the apparatus with ease. In addition, the cold cathode 101only needs to emit electrons in such a manner as to allow only a portionassociated with the hole 401 a in the shielding plate 401 to beirradiated with an electron beam E. Accordingly, power consumption iseasily reduced.

In the case of using the shielding plate 401 as described above, aconductor 403 may be provided around the hole 401 a as shown in FIG. 16,for example, and a given voltage may be applied to the conductor 403 sothat an electric field functioning as a lens is generated. Then, part ofan electron beam in the vicinity of the hole 401 a converges to alsostrike the storage film 105, so that the efficiency in utilizing anelectron beam is enhanced and a region smaller than the hole 401 a canbe irradiated with the electron beam. Instead of the conductor 403described above, the shielding plate 401 itself may have conductivity.

(Information Storage Apparatus Including a Plurality of InformationStorage Cells)

An information storage apparatus including a plurality of informationstorage cells 100 as described above and capable of writing and readinginformation at the same time will be described.

FIG. 17 is a perspective view showing a configuration of an informationstorage apparatus. In this information storage apparatus, theinformation storage cells 100 as shown in FIG. 1 are arranged in columnsand rows. More specifically, the information storage apparatus includesa substrate 121 in which a plurality of holes 121 a are formed and coldcathodes 101 similar to the cold cathode shown in FIG. 1 and othercomponents are provided in the respective holes 121 a. A storage film105 is provided above the substrate 121 such that a vacuum is createdbetween the substrate 121 and the storage film 105. (The substrate 121and the storage film 105 may be closely in contact with each other sothat the holes 121 a are individually kept under vacuum.)

Each four information storage cells 100 are determined as a group andfour bits of data is written and read out as one word at the same time.Specifically, as shown in FIG. 18, for example, each four informationstorage cells 100 (e.g., S00 through S03) are set as a group andconstitute a cell group 501 and a plurality of (e.g., four in theexample shown in the drawing) such cell groups 501 are provided.

Cathode line drivers 111 are associated with the respective cell groups501. One of the cathode ray drivers 111 is selected by an addressdecoder 502 for decoding two highest-order bits of a word address and anegative voltage (e.g., −5V) is applied to the cold cathodes 101 of theinformation storage cells 100 constituting the associated cell group501.

A deflection controlling circuit 114 is common to the informationstorage cells 100 in all the cell groups 501, generates a deflectingvoltage according to, for example, 14 lowest-order bits of the wordaddress and applies the voltage to deflection electrodes 104 in therespective information storage cells 100. (In a case where recordingpoints are arranged on the storage film 105 two-dimensionally, it issufficient that the above-mentioned lowest-order bits are furtherdivided and two deflecting voltages associated with the divided bits aregenerated.)

One acceleration controlling circuit 112 and one signal regenerator 115are common to the information storage cells 100 at the same bit positionin the respective cell groups 501.

In the information storage apparatus, to store data, a negative voltageis applied to the cold cathodes 101 of the information storage cells 100in one of the cell groups 501 in accordance with the two highest-orderbits of a word address. The acceleration controlling circuits 112 applyvoltages according to written data to the accelerating electrodes 102 inthe respective information storage cells 100. Accordingly, in a part ofthe storage film 105 associated with the information storage cells 100whose cold cathodes 101 have received the negative voltages, a regionassociated with 14 lowest-order bits of a word address is irradiatedwith electron beams at energy levels according to respective bits of thewritten data. Then, as already described with reference to FIG. 1, aphase change film 105 a is changed into an amorphous state or acrystallized state, thereby storing the written data accordingly.

On the other hand, to read stored data, the cathode ray drivers 111apply negative voltages to the cold cathodes 101 of the informationstorage cells 100 in some of the cell groups 501 associated with the twohighest-order bits of the word address. At the same time, theacceleration controlling circuits 112 apply given voltages to theaccelerating electrodes 102 in accordance with a read control signal.Then, an associated part of the storage film 105 is irradiated with anelectron beam at an energy level lower than that in writing, so that thevoltages at the detection electrodes 105 b are detected by the signalregenerators 115, thereby reading stored data.

As described above, writing or reading is performed at the same time ona plurality of (e.g., four) information storage cells 100 constitutingeach of the cell groups 501, so that high-speed access is achieved. Inaddition, one of the cell groups 501 is selected in accordance with apart of the address, so that data corresponding to words in a numberthat is equal to the number obtained by (the number of recording pointsin the respective information storage cells 100)×(the number of cellgroups 501.) That is, if 4×4 information storage cells 100 each capableof storing 128×128=16 Kbits of data are provided as shown in FIG. 18, aninformation storage apparatus capable of storing 64 Kwords×4 bits ofdata is obtained. If 1024×1024 information storage cells 100 eachcapable of storing 128×128=16 Kbits of data are provided on a 1μm-square recording plane, for example, a 1 mm-square storage film 105is capable of storing a large amount of 16 Gbits (about 10 Tbits/squareinches) of data at a high density.

In the foregoing example, each cell group 501 is constituted by fourinformation storage cells 100 arranged in a line (i.e., data is writtenin and read out from these cells at the same time.) Alternatively, eachcell group 501 may be constituted by information storage cells 100arranged in a plurality of lines. In this case, as long as theacceleration controlling circuit 112 and the signal regenerator 115associated with each information storage cell 100 are provided, data maybe written in and read out from all the information storage cells 100 atthe same time.

In the foregoing example, voltages to be applied to the cold cathodes101 are controlled in accordance with addresses whereas voltages to beapplied to the accelerating electrodes 102 are controlled in accordancewith written data. Alternatively, these voltages may be controlledconversely. Alternatively, only voltages to be applied to the coldcathodes 101 or the accelerating electrodes 102 may be controlled basedon addresses and written data, for example.

As described with reference to FIG. 15, in a case where a region to beirradiated with an electron beam by moving at least one of the shieldingplate 401 having a minute hole 401 a and the storage film 105 by theactuator 402, shielding plates 401 and/or storage films 105 of aplurality of information storage cells 100 may be moved by the sameactuator 402 or these components may be moved by actuators 402 using acommon control signal. Alternatively, the shielding plates 401 and/orthe storage film 105 for the plurality of information storage cells 100may be united.

(Servo Control of Electron-Beam Irradiated Position)

An example of an information storage apparatus in which an electron beamis controlled to be accurately applied to a region of the storage film105 associated with a storage bit will be described.

In addition to one or a plurality of information storage cells 100 asshown in FIG. 1, this information storage apparatus includes a servocell 600 as shown in FIG. 19. This servo cell 600 has a configurationsimilar to that of the information storage cells 100 but includes aninsulating film 611 and an anode 612 instead of the storage film 105.The insulating film 611 has minute holes 611 a formed in positionsassociated with respective storage bits. The anode 612 is connected toan applied-current detector 621 so that the amount of current caused toflow by an electron beam incident via the minute holes 611 a formed inthe insulating film 611 is detected. The result of the detection by theapplied-current detector 621 is input to a control amount adjustingcircuit 622. Given control signals are input from the control amountadjusting circuit 622 to an acceleration controlling circuit 112, aconvergence controlling circuit 113 and a deflection controlling circuit114. These control signals are also input to the accelerationcontrolling circuits 112, the convergence controlling circuits 113 andthe deflection controlling circuits 114 in the information storage cells100.

In the information storage apparatus with the foregoing configuration,calibration is performed on the amount of deflection and the state ofconvergence of an electron beam before data is stored or read out.Specifically, current distribution by the electron beam exhibits normaldistribution having the maximum value at its center, for example.Accordingly, with respect to current flowing in the anode 612 by anelectron beam incident on the anode 612 via each of the minute holes 611a, the center of the electron beam coincides with the center of theminute hole 611 a and the current is at the maximum when the beamdiameter of the electron beam at the insulating film 611 is at theminimum. In view of this, the amount of deflection and the degree ofconvergence are varied to small extent at every minute hole 611 a sothat an optimum value of the control amount at which the current flowingin the anode 612 is at the maximum is obtained and held in the controlamount adjusting circuit 622. Based on this optimum value, the controlamount adjusting circuit 622 outputs convergence control signals anddeflection control signals to the information storage cells 100 instoring and reading data. This ensures stable operation in whichvariation in configuration occurring in fabrication and variation indeflection amount due to variations of power supply voltage andtemperature and others are corrected.

More specifically, the calibration is performed by, for example, controloperation of the control amount adjusting circuit 622 in the followingmanner.

(1) First, the amount of deflection is adjusted to zero by setting avoltage applied to the deflection electrode 104 at zero. An electronbeam is generated so as to almost pass through a minute hole 611 aformed at (near) the center of the insulating film 611. Under thiscondition, a voltage applied to the convergence electrode 103 is changedso as to maximize current flowing in the anode 612, i.e., to cause theelectron beam to converge near the insulating film 611, so that currentdensity is enhanced.

(2) Next, the voltage applied to the deflection electrode 104 isslightly varied such that the current flowing in the anode 612 ismaximized, i.e., the minute hole 611 a is accurately irradiated with theelectron beam. (In a case where recording points are two-dimensionallyarranged, it is sufficient to deflect the electron beam to small extentin the X and Y directions alternately so as to maximize the current.)

(3) Then, the degree of convergence of the electron beam is adjusted inthe same manner as in (1).

Through (1) through (3), the position irradiated with the electron beamand the focal point of convergence are coincide with each other withrespect to the minute hole 611 a located at the center of the insulatingfilm 611.

(4) The amount of deflection is varied stepwise to a sufficiently smallamount at each step from the minimum to the maximum so that the electronbeam is gradually moved from an edge of a storage region to the other inthe storage film 105. In this way, a control amount at which the currentflowing in the anode 612 is at the maximum is obtained and is held inthe control amount adjusting circuit 622. That is, a deflection amountat which current flowing upon irradiation with an electron beam via eachminute hole 611 a formed through the insulating film 611 is at themaximum is obtained and held. A voltage applied to the convergenceelectrode 103 for each minute hole 611 a may also be controlled. Inaddition, voltages applied to the cold cathode 101 and the acceleratingelectrode 102 may also be controlled so as to reduce variation in theintensity of an electron beam.

In storing and reading data, control signals are input from the controlamount adjusting circuit 622 to the respective information storage cells100 based on the control amount held in the foregoing manner, so thathigh reproducibilities of the irradiated position and the degree ofconvergence of an electron beam are obtained and data is stored and readout with accuracy. Accordingly, the storage density is further increasedand, in addition, the efficiency in utilizing an electron beam is easilyenhanced.

In the foregoing example, the insulating film 611 having the minuteholes 611 a is used. However, the present invention is not limited tothis. A resistor or the like may be placed on, for example, the anode612 so as to detect current varying depending on the presence andabsence of the resistor or the like at the position irradiated with anelectron beam. Alternatively, a resistive film or a resistive platehaving a uniform resistivity may be provided and a position irradiatedwith an electron beam may be detected based on voltages near themidpoints of the respective four sides or vertexes, for example, so asto irradiate a given position with an electron beam. In the case ofensuring the accuracy in irradiating a relative position with anelectron beam with respect to each recording point, calibration asdescribed above may be performed only on one of the recording points sothat the amounts of deflection with respect to the other recordingpoints are controlled based on the calibration.

Only one servo cell 600 as described above may be provided in the entireinformation storage apparatus. In a case where a large number of theinformation storage cells 100 are provided, for example, the servo cell600 may be provided for each given number of information storage cells100.

The calibration is not necessarily performed before data is stored orread out in the manner as described above. Alternatively, feedbackcontrol may be performed on a position irradiated with an electron beamin the servo cell 600 with emission of electron beams in the informationstorage cells 100 suppressed, and then emission of the electron beams inthe information storage cells 100 may start when the irradiated positionin the servo cell 600 comes to a target position. In addition, aconductor or a slit may be provided at a reference position in theinsulating film 611 in the servo cell 600 or in the periphery of thestorage film 105 in the information storage cells 100 so as to performwriting or reading in accordance with a timing from the point of timewhen the conductor, for example, is irradiated with an electron beamduring scanning with the electron beam.

In a case where a phase change film or the like is used as a storagemedium as in the foregoing example, a nonvolatile information storageapparatus is obtained. However, the storage medium is not limited tothis and various components may be used.

Specifically, an insulator film, for example, may be used to utilize thepresence and absence of accumulated charge due to electron avalanche asdescribed in the description of the conventional technique.Alternatively, to store data, charge may be accumulated by injectingelectrons into a high-resistance film at low speed or electrons may beimplanted at high speed so that the accumulated charge is expelled byelectron avalanche. On the other hand, to read stored data, the presenceor absence of electron avalanche according to a charged state beforeirradiation with an electron beam may be detected depending on theamount of current. A component which changes its shape, e.g., comes tohave a hall therein or has its thickness reduced by thermal deformation,upon irradiation with a high-energy electron beam and causes currentflowing in an electrode at the backside to vary upon irradiation with alow-energy electron beam, such as a thin film made of a metal having alow melting point, may be used. In this case, a component made of aconductive material having a high resistivity, for example, ispreferably used so as to make current quickly escape when a portionhaving its thickness unchanged and other portions is irradiated with anelectron beam. Alternatively, a component such as a photonic materialwhich comes to have a fluorescent property by irradiation with ahigh-energy electron beam may be used so as to detect fluorescenceoccurring upon irradiation with a low-energy electron beam by using anoptical sensor.

The energy of an electron beam is not necessarily controlled by usingvoltages applied to the cold cathode 101 and the accelerating electrode102 and may be controlled by changing the duty ratio between pulsesapplied thereto and the number of such pulses or the diameter of a beamspot through adjustment of the degree of convergence, for example.

In a case where a plurality of information storage cells 100 areprovided, part of the cells may be used to store error detecting andcorrecting code. Specifically, as shown in FIG. 20, for example, out of1024 bits to be written and read out as, for example, one word at thesame time from a cell group 701 including 1024 information storage cells100, 64 bits may be used as parity bits (error detecting and correctingcode) for the other 960 bits so that error detection and errorcorrection are performed by a cyclic redundancy check (CRC) or otheroperations.

INDUSTRIAL APPLICABILITY

As described above, according to the present invention, a minute regionof a storage medium is irradiated with an electron beam emitted from acold cathode so that information is stored and read out. Accordingly, anarea necessary for storing one bit is greatly reduced and a large amountof information is stored at a high density. In addition, the apparatussize and power consumption are easily reduced and high-speed access isachieved. A plurality of bits of information is written and read out inparallel so that the speed is further increased. In addition, theposition irradiated with an electron beam is subjected to servo control,so that influences of variations in power supply voltage, temperatureand fabrication are reduced and high reliability is obtained. As aresult, irradiation of the storage medium with an electron beam iseffective for information storage apparatuses and others that store andread information.

1. An information storage apparatus comprising: a cold cathode electronbeam emitting part; a flat anode opposed to the cold cathode electronbeam emitting part; and a storage medium formed on the front or back ofthe anode and used for storing or reading information in accordance withirradiation with an electron beam emitted from the cold cathode electronbeam emitting part, wherein the cold cathode electron beam emitting partincludes a cold cathode placed in a chamber surrounded by a partitionand a film capable of transmitting an electron beam, and the inside ofthe chamber has a vacuum degree higher than a space sandwiched betweenthe film capable of transmitting an electron beam and the anode.
 2. Theinformation storage apparatus of claim 1, wherein an electron beam isaccelerated by application of a given voltage to the film capable oftransmitting an electron beam.
 3. An information storage apparatuscomprising: a cold cathode electron beam emitting part; a flat anodeopposed to the cold cathode electron beam emitting part; a storagemedium formed on the front or back of the anode and used for storing orreading information in accordance with irradiation with an electron beamemitted from the cold cathode electron beam emitting part; and anaccelerating part for accelerating the electron beam emitted from thecold cathode electron beam emitting part by using an electric field,wherein the accelerating part includes a plurality of electrodes towhich voltages with different phases are respectively applied, and theaccelerating part is configured to accelerate the electron beam bygenerating a moving electric field.
 4. An information storage apparatuscomprising: a cold cathode electron beam emitting part; a flat anodeopposed to the cold cathode electron beam emitting part; and a storagemedium formed on the front or back of the anode and used for storing orreading information in accordance with irradiation with an electron beamemitted from the cold cathode electron beam emitting part, wherein thecold cathode electron beam emitting part includes a plurality ofelectron-beam emitting parts, and the electron-beam emitting parts emitrespective electron beams at different timings in accordance with adistance from a given center so as to cause the emitted electron beamsto converge.
 5. An information storage apparatus comprising: a coldcathode electron beam emitting part; a flat anode opposed to the coldcathode electron beam emitting part; a storage medium formed on thefront or back of the anode and used for storing or reading informationin accordance with irradiation with an electron beam emitted from thecold cathode electron beam emitting part; a shielding part including aplate member, having a minute hole and configured to generate anelectric field for causing the electron beam emitted from the coldcathode electron beam emitting part to converge and pass through theminute hole; and an actuator part for moving at least one of theshielding part and the storage medium along the surface of the other,wherein a plurality of regions of the storage medium are allowed to beselectively irradiated with the electron beam.
 6. The informationstorage apparatus of claim 5, wherein the shielding part is configuredto generate an electric field for causing the electron beam to convergeand pass through the minute hole by application of a voltage to one ofthe plate member having conductivity and a conductive member provided onthe plate member.
 7. An information storage apparatus comprising: aplurality of cold cathode electron beam emitting parts; a flat anodeopposed to the cold cathode electron beam emitting parts; a storagemedium formed on the front or back of the anode and used for storing orreading information in accordance with irradiation with electron beamsemitted from the cold cathode electron beam emitting parts; a pluralityof convergence parts for causing each of the electron beams emitted fromthe cold cathode electron beam emitting parts to converge by using anelectric field or a magnetic field; and a plurality of deflection partsfor deflecting each of the electron beams by using an electric field ora magnetic field, wherein the deflection parts and the convergence partsare configured to cause deflection and convergence of the electron beamsemitted from the cold cathode electron beam emitting parts in accordancewith a common control signal so that a plurality of bits of informationis stored and read out at the same time in/from a plurality of regionsof the storage medium.
 8. An information storage apparatus comprising: aplurality of cold cathode electron beam emitting parts; a flat anodeopposed to the cold cathode electron beam emitting parts; a storagemedium formed on the front or back of the anode and used for storing orreading information in accordance with irradiation with electron beamsemitted from the cold cathode electron beam emitting parts; a shieldingpart for partly transmitting each of the electron beams emitted from thecold cathode electron beam emitting parts; and an actuator part formoving at least one of the shielding part and the storage medium alongthe surface of the other in accordance with a control signal for eachmoving direction, wherein a plurality of bits of information is storedor read out at the same time in/from a plurality of regions of thestorage medium.
 9. The information storage apparatus of claim 8, whereinthe shielding part includes a plate member having a plurality of minuteholes associated with the respective electron beams.
 10. The informationstorage apparatus of claim 8, further comprising anirradiated-position-shift detecting part for detecting a shift between agiven reference position and a position in the storage medium irradiatedwith each of the electron beams in accordance with the movement of saidone of the shielding part and the storage medium by the actuator part,wherein the position irradiated with each of the electron beams iscontrolled by the actuator part in accordance with a result of thedetection by the irradiated-position-shift detecting part.
 11. Theinformation storage apparatus of claim 7, further comprising: anirradiated-position detecting part for detecting a shift from a givenreference position in accordance with a detection signal obtained when airradiated-position detecting portion provided in part of the storagemedium is irradiated with an electron beam emitted from at least one ofthe cold cathode electron beam emitting parts, wherein the positionirradiated with the electron beam is controlled by the deflection partsand the convergence parts with respect to one or more electron beamsemitted from the other cold cathode electron beam emitting parts inaccordance with a result of the detection by the irradiated-positiondetecting part.
 12. The information storage apparatus of claim 10,wherein the irradiated-position-shift detecting part is configured todetect a shift between a given reference position and a position in thestorage medium irradiated with at least one electron beam emitted fromat least one of the cold cathode electron beam emitting parts, and theposition irradiated with the electron beam is controlled by the actuatorpart with respect to one or more electron beams emitted from the othercold cathode electron beam emitting parts in accordance with a result ofthe detection by the irradiated-position-shift detecting part.
 13. Theinformation storage apparatus of claim 7, wherein an electron beamemitted from a part of the cold cathode electron beam emitting parts isused to store and read at least one of error detecting code and errorcorrecting code in storing or reading of information by using one ormore electron beams emitted from the other cold cathode electron beamemitting parts.
 14. The information storage apparatus of claim 8,wherein an electron beam emitted from a part of the cold cathodeelectron beam emitting parts is used to store or read at least one oferror detecting code and error correcting code in storing or reading ofinformation by using one or more electron beams emitted from the othercold cathode electron beam emitting parts.
 15. The information storageapparatus of claim 11, wherein the irradiation-position detectingportion is a portion including a plurality of minute holes formed in thestorage medium, and the irradiated-position detecting part is configuredto detect current flowing through the minute holes and perform leaningcontrol in such a manner that control amounts of deflection andconvergence at which current is largest is defined as control amounts ofdeflection and convergence at which a shift from the reference positionis smallest.
 16. A method for storing information using an informationstorage apparatus comprising: a cold cathode electron beam emittingpart; a flat anode opposed to the cold cathode electron beam emittingpart; a storage medium formed on the front or back of the anode and usedfor storing or reading information in accordance with irradiation withan electron beam emitted from the cold cathode electron beam emittingpart; and an accelerating part for accelerating the electron beamemitted from the cold cathode electron beam emitting part by using anelectric field, wherein a moving electric field is generated by applyingvoltages with different phases to a plurality of electrodes of theaccelerating part, thereby accelerating the electron beam.
 17. A methodfor storing information using an information storage apparatuscomprising: a cold cathode electron beam emitting part; a flat anodeopposed to the cold cathode electron beam emitting part; and a storagemedium formed on the front or back of the anode and used for storing orreading information in accordance with irradiation with an electron beamemitted from the cold cathode electron beam emitting part, wherein aplurality of electron-beam emitting parts of the cold cathode electronbeam emitting part emit respective electron beams at different timingsin accordance with a distance from a given center so as to cause theemitted electron beams to converge.
 18. A method for storing informationusing an information storage apparatus comprising: a cold cathodeelectron beam emitting part; a flat anode opposed to the cold cathodeelectron beam emitting part; and a storage medium formed on the front orback of the anode and used for storing or reading information inaccordance with irradiation with an electron beam emitted from the coldcathode electron beam emitting part, wherein a shielding part includinga plate member having a minute hole generates an electric field forcausing the electron beam emitted from the cold cathode electron beamemitting part to converge and pass through the minute hole, and anactuator part causes at least one of the shielding part and the storagemedium to move along the surface of the other so that a plurality ofregions of the storage medium are allowed to be selectively irradiatedwith the electron beam.
 19. A method for storing information using aninformation storage apparatus comprising: a plurality of cold cathodeelectron beam emitting parts; a flat anode opposed to the cold cathodeelectron beam emitting parts; a storage medium formed on the front orback of the anode and used for storing or reading information inaccordance with irradiation with electron beams emitted from the coldcathode electron beam emitting parts; a plurality of convergence partsfor causing each of the electron beams emitted from the cold cathodeelectron beam emitting parts to converge by using an electric field or amagnetic field; and a plurality of deflection parts for deflecting eachof the electron beams by using an electric field or a magnetic field,wherein the deflection parts and the convergence parts are controlled inaccordance with a common control signal to cause deflection andconvergence of the electron beams emitted from the cold cathode electronbeam emitting parts so that a plurality of bits of information is storedand read out at the same time in/from a plurality of regions of thestorage medium.
 20. A method for storing information using aninformation storage apparatus comprising: a plurality of cold cathodeelectron beam emitting parts; a flat anode opposed to the cold cathodeelectron beam emitting parts; a storage medium formed on the front orback of the anode and used for storing or reading information inaccordance with irradiation with electron beams emitted from the coldcathode electron beam emitting parts; a shielding part for partlytransmitting each of the electron beams emitted from the cold cathodeelectron beam emitting parts; and an actuator part for moving at leastone of the shielding part and the storage medium along the surface ofthe other, wherein the actuator part is driven in accordance with acontrol signal for each moving direction, and a plurality of bits ofinformation is stored or read out at the same time in/from a pluralityof regions of the storage medium.